text: The Copper Age, also called the Eneolithic or the Chalcolithic Age, has been traditionally understood as a transitional period between the Neolithic and the Bronze Age, in which a gradual introduction of the metal (native copper) took place, while stone was still the main resource utilized. Recent archaeology has found that the metal was not introduced so gradually and that this entailed significant social changes, such as developments in the type of habitation (larger villages, launching of fortifications), long-distance trade, and copper metallurgy.
  Some of the earliest Copper Age artifacts were found in the 5th and 6th millennia BCE archaeological sites of the Vinča culture such as Majdanpek, Jarmovac and Pločnik (including a copper axe from 5500 BCE). Somewhat later, in the 5th millennium BCE, metalwork is attested at Rudna Glava mine in Serbia, and at Ai Bunar mine in Bulgaria.
  3rd millennium BCE copper metalwork is attested in places like Palmela (Portugal), Cortes (Navarre), and Stonehenge (England). However, as often happens with the prehistoric times, the limits of the age cannot be clearly defined and vary between different sources.